Interstitium is the Fluid-Filled space around the alveoli or air sacs of the lungs. Interstitial lung disease (a.k.a: Diffuse Parenchymal Lung Disease) is a very rare condition. It is a group of lung disorders that commonly affect interstitium. This disease interferes with gas exchange. In this condition, fibrosis and inflammation of parenchyma occurs.
Interstitial lung disease can be acute or chronic and irreversible. Common types of interstitial lung diseases are:
- Idiopathic pulmonary fibrosis
- Hypersensitivity pneumonitis such as bird-fancier’s lung and farmer’s lung
- Medication-induced disease
- Nonspecific interstitial pneumonitis associated with other autoimmune diseases
- Interstitial pneumonia that occur due to bacteria, viruses, or fungi
Among these, idiopathic pulmonary fibrosis is the most common condition. It is commonly seen in older people. It is the most severe and devastating condition as early diagnosis is difficult.
What Causes Interstitial Lung Disease?
Generally, the cause of interstitial lung disease is unknown (idiopathic). However, it can also occur due to other causes such as:
- Other connective tissue diseases such as systemic lupus erythematosus, rheumatoid arthritis and sarcoidosis
- Use of medications such as bleomycin and methotrexate
- Occupational exposure to chemicals such as asbestos fibres, talc, coal dust, and cotton dust
- Genetic abnormalities such as Hermansky-Pudlak syndrome
The inflammation in the lung can be triggered by any of the causes mentioned above. When interstitium of the lung is damaged due to inflammation, oxygen supply to the bloodstream is hindered. The inflammatory cells infiltrate into alveoli leading to thickening of the alveolar wall. The inflammatory mediators can also trigger fibrosis (scarring of the tissue). This condition alters the shape of lungs as there will be a distortion of the normal structure of alveoli. The lungs look smaller and stiffer in this disease.
Symptoms of Interstitial Lung Disease:
Symptoms of interstitial lung disease may vary depending on age, gender, geographical factors, or other factors. Common respiratory symptoms that appear are shortness of breath and cough. In initial stages, shortness of breath can be only during exertion but in advanced stages, it can also occur during rest. Other symptoms that may be seen are:
- Clubbing of nails
- Weight loss
- Joint pain
- Exercise intolerance
Risk Factors of Interstitial Lung Disease:
Interstitial lung disease is commonly seen in adults. The risk increases with advancing age. It may also occur in infants and children but very rarely. Family history or hereditary factors can also influence interstitial lung disease. Other risk factors include:
- Smoking (active smoking can worsen the condition)
- Exposure to toxins during farming, construction, stone cutting, or working in metal industries
- Air pollution due to smoke from the vehicles or industries
- Radiation therapy to the chest (lung or breast)
- Chemotherapy or immunomodulatory agents
- Use of antibiotics such as nitrofurantoin
- Use of cardiovascular drugs such as amiodarone
- Epstein-barr virus
Complications of Interstitial Lung Disease:
Complications of interstitial lung disease are:
- Hypoxemia: It is a condition in which oxygen levels are reduced both at rest and with exertion.
- Acute Exacerbation (Worsening of Symptoms): It is a severe complication with abrupt onset and also may require hospitalization.
- Pulmonary Hypertension: It is a serious progressive disease that may result in cor pulmonale (failure of the right side of the heart).
- Respiratory Failure: It is the end stage interstitial lung disease that may lead to death.
Diagnosis of Interstitial Lung Disease:
The healthcare provider evaluates the signs and symptoms during physical examination. Diagnostic tests are performed to identify the stage of disease and plan treatment.
Chest X-ray: It is an imaging test in which the X-rays are used to view the lung. However, the X-ray appears to be normal in early stages. Opacity in the lung can be viewed in case of advanced disease.
High Resolution Computed Tomography (HRCT) Scan: Computed tomography scan is performed with high resolution to provide a detailed view of the lung.
Pulmonary Function Tests (PFT): These tests help to evaluate the lung function using spirometry. These tests help to determine breathing patterns, lung volumes, and lung capacities. The total lung capacity is usually decreased in this condition.
Lung Biopsy: It is the procedure in which a sample of lung tissue is obtained to examine under the microscope. The sample can be obtained through bronchoscopy or surgery. This test helps in definitive diagnosis of interstitial lung disease. Patients with high fibrosis are categorized into advanced stage and they have poor prognosis whereas patients with high inflammation respond to treatment very well and have good prognosis.
Treatments for Interstitial Lung Disease:
Treatment for interstitial lung disease depends on the type and its underlying cause.
- Antibiotics: These medications can be given if interstitial pneumonia is caused by bacteria. Antifungal agents are given to treat pneumonia caused by fungus. Viral pneumonias don’t require any treatment.
- Corticosteroids: Prednisone and methylprednisolone can be prescribed to reduce the inflammation.
- Immunosuppressive agents: Azathioprine and cyclophosphamide can be given to treat inflammation and reduce its progression to fibrosis.
- Pirfenidone: It can be given to treat idiopathic pulmonary fibrosis.
- Oxygen Therapy: It can be given to treat hypoxemia and reduce the damage that occurs due to low oxygen levels.
- Lung Transplantation: It is performed if the disease doesn’t resolve with the treatment usually in cases of advanced or end stage interstitial lung disease. However, it is opted only for selected patients depending on their overall health.
- Pulmonary Rehabilitation: It is a health management program that includes education, exercise, and support for patients with chronic lung diseases. Breathing techniques, training about exercise, psychological counselling, and nutritional counselling are provided during this program.
Prevention of Interstitial Lung Disease:
To prevent interstitial lung disease, it is essential to quit smoking. Avoiding exposure to smoke, dust, mould, and other toxic chemicals can also help in prevention.
Consume a healthy diet and maintain normal weight. Get vaccinated against respiratory infections such as pneumonia.
Treating the infections promptly and education about the disease is also necessary.